1. Field of the Invention
This invention relates to a throttle device for an internal-combustion engine and, more particularly, to an electronically controlled throttle device which controls the opening and closing operation of a throttle valve by driving an electric actuator according to a control signal.
2. Description of Related Art
An electronically controlled throttle device which controls an engine throttle valve by driving an electric actuator (e.g., a dc motor and a stepping motor) has been in actual use. The electronically controlled throttle device is used to control the amount of opening of the throttle valve to the optimum throttle opening for engine operating condition in accordance with an accelerator pedal opening signal and a traction control signal. In the throttle body, therefore, a sensor which is a so-called throttle sensor for detecting a throttle valve opening (throttle position) is mounted.
The throttle sensor generally adopted is a potentiometer type, in which a brush mounted on a rotor rotating together with a throttle valve shaft slides on a resistor provided on a substrate, thereby to output a potentiometer signal (sensor detection signal) corresponding to the throttle valve opening.
The throttle body is equipped with an electric actuator and a reduction gear mechanism for power transmission, and recently is further provided with a default opening setting mechanism for holding a wider initial opening (the default opening) of the throttle valve than the full-close position when the ignition switch is in off position (in other words, when no current is being supplied to the electric actuator).
Here, the full-closed position of the throttle valve is defined as a mechanically full-closed position and an electrically full-closed position. The mechanically full-closed position is the minimum opening position of the throttle valve defined by a stopper. The minimum opening is set at a position where the intake air passage is slightly opened from a full-closed position to thereby prevent the throttle valve from galling. The electrically full-closed position is the minimum opening position within the range of opening used in control, and is set, by the control of the electric actuator, at a position of a slightly wider opening than the mechanically full-closed position (e.g., about 1 deg. larger than the mechanically full-closed position).
The default opening (i.e., the initial opening when the ignition switch is in off position) is set to the amount of opening of the throttle valve which is opened wider than the above-described full-closed position (the mechanically full-closed position and the electrically full-closed position) (e.g., 4 to 13 deg. wider than the mechanically full-closed position). The default opening is set from the reasons: one for achieving the air flow rate necessary for fuel combustion for operation to be performed prior to engine warm-up at the time of engine starting (cold starting) without providing an auxiliary air passage (an air passage bypassing the throttle valve). During idling, the throttle valve is controlled towards decreasing the amount of opening from the default opening as the engine warm-up proceeds (in this case, the electrically full-closed position is the lower limit position). For another reason, the default opening is adopted to meet requirements for insuring self-running (limping home) in the event of a throttle control system trouble or insuring an intake air flow rate necessary for preventing an engine stall, and for preventing the throttle valve from being stuck with a viscous substance, ice, or other, on the inside wall of the throttle body.
As examples of the electronically controlled throttle device, known prior art has been stated in, for example, Japanese Laid-Open No. Sho 63-150449 Patent Publication, U.S. Pat. No. 4,947,815 specification , Japanese Translation of PCT Application No. Hei 2-500677 corresponding to the U.S. Patent, Japanese Laid Open No. Sho 62-82238 Patent Publication and its corresponding U.S. Pat. No. 4,735,179 specification, Japanese Laid-Open No. Hei 10-89096 Patent Publication, and Japanese Laid Open No. Hei 10-131771 Patent Publication.
The electronically controlled throttle device can control more accurately the air flow rate suitable for the operation of the internal-combustion engine than the mechanical throttle device which transmits the amount of depression of the accelerator pedal to the throttle valve shaft through an accelerator cable. The component count is increased because of the provision of an electric actuator, a default opening setting mechanism, and a throttle sensor. Therefore, downsizing, weight reduction and simplification of the throttle body, and further improvements in operation accuracy are demanded.
In order to solve the above-described problem, it is an object of this invention to provide a throttle device for an internal-combustion engine which has been reduced in size and weight, simplified in assembly and wiring harness, and further improved in operation stability and accuracy of the throttle sensor.
This invention has basically the following constitution.
The first aspect of the invention pertains to an electronically controlled throttle device equipped with an electric actuator.
In this electronically controlled throttle device, a mounting space is formed, on one surface of the throttle body side wall, for mounting a reduction gear which transmits the power of the electric actuator to a throttle valve shaft; a gear cover for covering the reduction gear mechanism is provided; and a throttle sensor for detecting the throttle valve opening is built inside of the gear cover and covered with a sensor cover.
A rotor shaft hole of the throttle sensor is exposed out through the sensor cover; when the gear cover is mounted on the side wall of the throttle body, one end of the throttle valve shaft fits in the rotor shaft hole.
According to the constitution stated above, a complete set of components of the throttle sensor can be assembled by installing only on the gear cover side. As the gear cover is attached on the side wall of the throttle body, the forward end of the throttle valve shaft goes into engagement with the rotor shaft hole of the throttle sensor, and besides the throttle valve shaft and the throttle sensor can easily be engaged by a single operation. Furthermore, the throttle sensor, concealedly covered with the sensor cover under the gear cover, can be protected from dust. It is, therefore, possible to prevent entrance of dust and abrasion particles of components into the throttle device if the gear cover is either on or off, thus insuring improved sensor reliability.
Furthermore, it is proposed that, under the optimum condition, one end of the throttle valve shaft fits in the rotor shaft hole, elastically deforming a spring (fitting spring) inserted in the shaft hole, and the rotor is retained by a rotor retaining spring interposed between the rotor and the sensor cover.
Let F1 be the spring force of the fitting spring which acts on the throttle valve shaft, F2 be the spring force of the rotor retaining spring, and F3 be the spring force F1 of the fitting spring multiplied by the coefficient of friction "sgr"1 between the throttle valve shaft and the shaft hole, and F1 and F2 load are so set as to achieve the relation of F2 greater than F3.
Also, let F4 be a turning torque required to turn the rotor (F4=the spring force F2 of the rotor retaining springxc3x97the force of friction "sgr"2 during rotor-rotation), and let F5 be the turning torque against the spring force F1 of the fitting spring, and the F1 and F2 load are set so as to have the relation of F5 greater than F4.
Because of the relation of F2 greater than F3, the rotor can be constantly kept in a given position despite of axial vibration of the throttle valve shaft, and a chattering of the throttle sensor output can be reduced.
Furthermore, because of the relation of F5 greater than F4, it is possible to insure smooth rotation of the rotor in relation to the rotation of the throttle valve shaft, and also to improve the responsivity of sensor output.
The second aspect of the invention pertains to the electronically controlled throttle device, in which one end of the throttle valve shaft projects out of the side wall of the throttle body into engagement with the rotor of the throttle sensor for detecting the throttle valve opening; and the other end of the throttle valve shaft also projects out of the side wall of the throttle body and has a flat surface in this projecting portion.
According to the constitution described above, it becomes possible to check the output characteristic of the throttle sensor of the throttle valve shaft by giving a turning torque from outside to the throttle sensor by using an inspection jig engaged with the end portion of the throttle valve shaft on the opposite side of the throttle sensor.
The third aspect of invention pertains to the electronically controlled throttle device, in which, on one surface of the throttle body side wall, a space is formed for mounting the reduction gear mechanism which transmits the power of the electric actuator to the throttle valve shaft, and the motor terminal of the electric actuator is disposed appearing into the space for mounting the reduction gear mechanism. In the meantime, embedded by resin molding in the gear cover made of a synthetic resin for covering the reduction gear mechanism mounting space is a conductor, one end of which serves as a connector terminal for connection with the external power source, while the other end serves as a connecting terminal for connection with the motor terminal of the electric actuator. The connecting terminal protrudes out into the interior of the gear cover, being connected with the motor terminal through a joint-type connecting hardware.
According to the above-described constitution, the connector terminal for connection with the external power source and the conductor of the connecting terminal for connection with the motor terminal are embedded in the gear cover; and therefore it is possible to easily connect the connecting terminal on the gear cover side, which is in connection with the external power source, to the motor terminal on the throttle body side through the joint-type connecting hardware in the gear cover by saving manpower required for wiring these terminals and besides by mounting the gear cover to the throttle body.